Recently, a method of retrieving desired musical composition data from many items of musical composition data stored in a high-capacity storage means, such as a hard disk, and playing back the music has been popular. Such retrieving of musical composition data can use bibliographic data, such as the artist names, the song titles, and the like, as retrieval data, and, in addition to the bibliographic data, the emotions of musical compositions, such as up-tempo songs and slow-tempo songs. This detects the features of musical compositions from musical composition data, and retrieves musical composition data by matching the detected features with the emotions of musical compositions.
Tempos are one of the features that can be matched with the emotions of musical compositions. Because the tempo is an important parameter of a musical composition, various detecting methods have been proposed.
For example, a first patent document discloses a technology that measures a peak interval between the amplitudes, each of which has with a predetermined frequency component, in a music signal to thereby detect the tempo.
In addition, for example, a second patent document obtains correlations among level changes in a music signal at preset intervals, and seeks the time interval with the highest correlation function to thereby detect the tempo.
In addition to the methods for detecting the tempo by analyzing a music signal in the time domain, methods for detecting the tempo by analyzing a music signal in the frequency domain are disclosed.
For example, a third patent document discloses a technology that performs a Fast Fourier transform on a music signal in a micro section to obtain average power, and performs a Fast Fourier transform on time-series data of the average power to calculate a power spectrum. Then, the technology detects the tempo based on the difference between the calculated power spectrum and an approximate line of the power spectrum.
First patent document: Japanese Patent Laid-Open No. H8-201542
Second patent document Japanese Patent Laid-Open No. H5-27751
Third patent document Japanese Patent Laid-Open No. 2006-194953